Engine races on 1990 Honda

The engine on my 1990 is racing--reving up to 2000 rpms then dropping
back to 1000 rpms--continuously while in drive and also while idling.
Any ideas what could be causing this problem and how to fix it?

 

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Sometimes just filling the coolant reservoir (and rad) will be enough to
solve that problem. (air in system) You'll have to check it again next
evening after the engine cools, and fill it to the MAX line again. Even
if it doesn't solve the problem at least you're better prepared for
winter driving.

'Curly'

 

The likely list of suspects:

Air bubble in your cooling system
Vacuum leak
Idle Air Control Valve
Fast Idle Thermo Valve

 

A large air leak normally causes this.

Fast Idle Valve is the first culprit.

When did this start?

 

Thanks for responding. It started maybe a week ago. Last night I
added coolant (gotta remember to check those fluid levels from now on)
and it works great now!

 

Thanks for all the responses. I added coolant and it works great now!

 

I know on the previous generation (86-89) this was a veeery common
culprit. 50 bucks at a yard, pliers, ratchet, maybe 20 minutes.
bada-boom, bada-bing.